The present invention relates generally to bicycle components and more specifically to bicycle crank assemblies.
Presently, bicycles have grown to a high level of popularity and many bicycles are highly specialized for certain applications. These specialized applications impose extraordinary requirements on various bicycle components. Despite these extraordinary requirements, many of the basic bicycle components have remained relatively unchanged for quite some time. For occasional riders, bicycles in their present form may be sufficient. However, specialty bicycles such as mountain bikes, racing bikes, daily commute bikes, and other specialized bikes have many components that could be significantly improved. One such component is the bicycle crank assembly.
Current crank assemblies are made up of a spindle that is mounted within a bottom bracket of a bicycle frame for rotation about a crank assembly rotational axis. Right and left crank arms are attached to the spindle and right and left pedals are attached to the ends of the right and left crank arms. The crank arms and spindle are often subjected to substantial stresses. Often times the rider has minimal time to react to changing trail or road conditions such as rough terrain or potholes. These jarring trail and road conditions place a heavy burden upon the mechanical integrity of the crank assembly.
The pedals, crank arms, and spindle have the severe task of carrying the majority of the rider's weight, the impact loads caused by rough terrain, as well as transforming the riders leg motions into the torque that propels the rider and the bicycle. Therefore, the crank assembly is subjected to a significant amount of torque. The continuous cranking motion, combined with the high degree of torque, over an extended period of time, causes wear and may eventually lead to the failure of the crank arm and/or the point where the crank arm connects to the spindle.
The most widely accepted crank arm/spindle connection system currently available is a system that utilizes a right and left crank arm, usually made of an aluminum alloy, and a hardened steel or titanium spindle. The spindle has four flats machined at a slight angle on each end of the spindle creating a tapered protruding square. The tapered protruding square usually is about 1/2" to 5/7" in length. The crank arm has a mating tapered square cavity formed into one end of the crank arm. The attachment of the crank arm to the spindle is achieved by pressing the tapered square cavity of the crank arm over the tapered square protrusion of the spindle. This press fit typically relies on distortion at the points of contact between the crank and the spindle to hold the crank arm engaged with the spindle. A nut or bolt is also typically tightened against the outer portion of the crank arm to hold the crank arm onto the spindle.
While the tapered square configuration may seem at first glance a viable and economical method of attaching the crank arms to the spindle, it suffers in one major area. Although the tapered square may adequately transfer the torque from the rider to drive system, it does not do a very good job of preventing the crank arm from rocking or oscillating on the spindle. This oscillating motion in which the crank arm rocks independently of the spindle occurs because of the excessive, and constantly changing loads imposed on the crank system.
With continued use, the oscillating motion may deform the shape of the tapered square 20 connection system. Once enough deformation occurs, the crank arms become useless. There are shapes other than tapered squares that are currently used to transfer of torque between the crank arm and the spindle such as a spline or a tapered spline. Some include a spline in conjunction with a clamping arrangement that further tightens the splined portion of the crank arm around the mating splined portion of the spindle. Regardless of the shape used in transferring torque from the crank arm through the spindle to the other crank arm, all of the systems could be improved through a system that would eliminate the independent oscillating movement of the crank arms on the spindle.
Additionally, with the tapered square configuration, a crank arm puller is typically required in order to remove the crank arms from the spindle. This is a difficult and time consuming procedure. Many bicyclists are not willing to take on this procedure and therefore this configuration discourages the proper servicing of the spindle components such as spindle bearings. Also, in the case of racing bikes, a broken crank arm or spindle of this type during the course of a race virtually insures that the racer is out of the race due to the time required to change the spindle or crank arm.
The present invention discloses an improved crank arm/spindle connection arrangement that utilizes two spaced apart load bearing surfaces for interconnecting two separate spindle portions. The two spaced apart load bearing surfaces provide a stabilized connection arrangement for interconnecting the two spindle portions. A novel spline arrangement is also disclosed for interconnecting the two spindle portions. This two piece spindle arrangement eliminates the conventional connection points between each of the crank arms and the spindle.
Another problem with conventional crank arm systems is that the chain rings that are driven by the crank arms are typically attached to the inside of the crank arms. Because of this configuration, the crank arm typically needs to be removed in order to remove the chain rings. As mentioned above, since a crank puller is typically required to remove the crank arm, it is difficult to quickly remove and replace a chain ring. The present invention discloses a quick change chain ring arrangement that allows the chain ring to be removed and replaced without requiring the crank arm to be removed.
In conventional crank assemblies, the chain rings are typically fixed to the associated crank arm as mentioned above. Because of this, it can be difficult to properly align the chain rings with other bicycle components such as a front derailleur. Often times, a specialty bike is assembled from components provided by a variety of manufacturers. These manufacturers often have varying spacing and positioning requirements for their components. This further contributes to the difficulties in properly aligning the various components of the bicycle. The present invention discloses a chain ring alignment system that allows the position of the chain rings of the crank assembly to be adjusted along the crank assembly rotational axis.
In many circumstances, it would be desirable to provide crank arms with a larger crank arm radius. This would provide greater leverage to the rider and allow more driving force to be exerted for a given amount of effort from the rider. However, the length of the crank arms of conventional crank assemblies are limited by the ground clearance of the crank arms. Also, as the crank arm radius is increased, the rider must move the pedals around a larger circumference which takes a longer amount of time. This takes away from the leverage benefits provided by longer crank arms. The present invention discloses a variable length crank arm arrangement that allows the crank arm length to be increased during the downward stroke of the crank arm rotation and shortened during the upward stroke. This increases the leverage available to the rider during the downward stroke of the pedal rotation as would be the case with a longer fixed crank arm However, the variable length crank arm reduces the distance the pedal is required to travel during a crank assembly rotation compared to a longer fixed crank. Furthermore, the variable length crank arm arrangement may be configured to increase the ground clearance of the crank assembly.
Another problem associated with conventional crank assemblies involves currently available arrangements for connecting a bicycle shoe to a pedal. Typically, bicycle shoes include a clip for attaching the shoe to the pedal. These clips are normally engaged by properly aligning the clip on the shoe with an associated protrusion on one of the flats of the pedal. This arrangement requires the rider to first position the pedal with the protrusion facing up and then align the clip on the shoe with the protrusion before engaging the clip. This can be an awkward procedure that can at times be dangerous. Also, once clipped in, the connection may be difficult to quickly disengage causing potential safety concerns. The present invention discloses a bicycle shoe to pedal connection arrangement that simplifies the process of engaging and disengaging the shoe to pedal connection.